Improved animation when sending messages

Author: martinmitrevski

Sources/StreamChatSwiftUI/ChatChannel/ChatChannelViewModel.swift

@@ -173,11 +173,12 @@ open class ChatChannelViewModel: ObservableObject, MessagesDataSource {
             array.append(message)
             self.messages = LazyCachedMapCollection(source: array, map: { $0 })
         } else {
-            if shouldAnimate(changes: changes) {
+            let animationState = shouldAnimate(changes: changes)
+            if animationState == .animated {
                 withAnimation {
                     self.messages = messages
                 }
-            } else {
+            } else if animationState == .notAnimated {
                 self.messages = messages
             }
         }
@@ -364,22 +365,32 @@ open class ChatChannelViewModel: ObservableObject, MessagesDataSource {
         }
     }
 
-    private func shouldAnimate(changes: [ListChange<ChatMessage>]) -> Bool {
+    private func shouldAnimate(changes: [ListChange<ChatMessage>]) -> AnimationChange {
         if !utils.messageListConfig.messageDisplayOptions.animateChanges {
-            return false
+            return .notAnimated
         }
 
+        var skipChanges = true
         for change in changes {
             switch change {
             case .insert(_, index: _),
                  .remove(_, index: _):
-                return true
+                return .animated
+            case let .update(message, index: index):
+                if index.row < messages.count,
+                   message.messageId != messages[index.row].messageId {
+                    skipChanges = false
+                }
             default:
-                log.debug("detected non-animatable change")
+                skipChanges = false
             }
         }
 
-        return false
+        if skipChanges {
+            return .skip
+        }
+        
+        return .notAnimated
     }
 
     private func enableDateIndicator() {
@@ -468,3 +479,9 @@ public enum ChannelHeaderType {
     /// The header shown when someone is typing.
     case typingIndicator
 }
+
+enum AnimationChange {
+    case animated
+    case notAnimated
+    case skip
+}

StreamChatSwiftUITests/Tests/ChatChannel/ChatChannelViewModel_Tests.swift

@@ -233,6 +233,67 @@ class ChatChannelViewModel_Tests: StreamChatTestCase {
         XCTAssert(headerType == .typingIndicator)
     }
 
+    func test_chatChannelVM_skipChanges() {
+        // Given
+        let channelController = makeChannelController()
+        let viewModel = ChatChannelViewModel(channelController: channelController)
+        let messageId = String.unique
+        let message = ChatMessage.mock(
+            id: messageId,
+            cid: .unique,
+            text: "Some text",
+            author: .mock(id: .unique)
+        )
+        
+        // When
+        channelController.simulate(
+            messages: [message],
+            changes: [.update(message, index: .init(row: 0, section: 0))]
+        )
+        let initial = viewModel.messages
+        channelController.simulate(
+            messages: [message],
+            changes: [.update(message, index: .init(row: 0, section: 0))]
+        )
+        let after = viewModel.messages
+        
+        // Then
+        XCTAssert(initial[0].messageId == after[0].messageId)
+    }
+    
+    func test_chatChannelVM_animatedChanges() {
+        // Given
+        let channelController = makeChannelController()
+        let viewModel = ChatChannelViewModel(channelController: channelController)
+        let message = ChatMessage.mock(
+            id: .unique,
+            cid: .unique,
+            text: "Some text",
+            author: .mock(id: .unique)
+        )
+        let newMessage = ChatMessage.mock(
+            id: .unique,
+            cid: .unique,
+            text: "New message",
+            author: .mock(id: .unique)
+        )
+        
+        // When
+        channelController.simulate(
+            messages: [message],
+            changes: [.update(message, index: .init(row: 0, section: 0))]
+        )
+        let initial = viewModel.messages
+        channelController.simulate(
+            messages: [message, newMessage],
+            changes: [.insert(newMessage, index: .init(row: 1, section: 0))]
+        )
+        let after = viewModel.messages
+        
+        // Then
+        XCTAssert(initial.count < after.count)
+    }
+    
     // MARK: - private
 
     private func makeChannelController(